Three-dimensional finite-difference tomography of velocity structure of the upper crustal in North China

We parameterized velocity model of North China using square nets. In the velocity model total 649 x 890 x 16 grid points are included with grid spacing of 1.0 km. Three dimensional finite-difference inversion method is used to obtain 3-D velocity structure of the upper crust in North China by means of Pg wave data from 30 deep seismic sounding (DSS) profiles in the studied area. The inversion results revealed that the low velocity rhomb-shaped North China basin is surrounded by high velocity uplifts, and North China basin is comprised of two large fault zones with an uplift in between. The two large fault zones are divided into several small basins. There are many shovel-like normal faults in the studied area, and the depth of crystalline basement varies significantly at different geological structures. All of these results suggest that North China has very complicated geological structure and it has the deep structural background for strong earthquakes.